Cabinet for housing sound-reproducing apparatus



July 1, 1941. r H. F. voLsoN CABINETVFOR HOUSING soUND-RRonUCING' APPARATUS Filedy July 31, 1940 2 Sheets-.Sheet- 1 mz Z July l, 1941.l y H. F. oLsoN CABINET FOR HOUSING SOUND-REPRODUCING APPARATUS shuts-sheet 2 I Filed July .31.,` i940 /9 y0 l la;

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Patente-dJuly 1, 1941 CABINET FOR HOUSING SOUND-REPRO- iv DUCING APPARATUS Harry F. vlson, Haddon Heights, N. J., assigner to Radio Corporation of. America, a corporation of Delaware I Application July 3l, 1940, Serial No. 348,632

' mi, srs-2i 14 Claims.

This invention relates to cabinets for housing l sound-reproducing apparatus, and more particularly to an acoustic filter therein .for attenuating sounds of certain frequencies reproduced by phonographs housed therein, the present invention vbeing an improvement over that disclosed and claimed in the copending application of `Alexander D. Burt, Serial No. 343,107, filed June 29, 1940, and assigned to Radio Corporation of America.

The term phonograph" is usually applied to a system in which a needle 'follows the undulations in the groove of a record and transforms the undulations into `corresponding acoustical or electrical variations. In\ the case of a phonograph employing the combination of a pickup, an amplifier and a loudspeaker, the mechanical variations due to the motion ofthe needlev carried by the pickup are transferred to the mechanoelectrical transducer and are transformed into corresponding electrical variations. The vibration ofthe various elements of the pickup and the vibration of the record itself due to the'interaction between the needle and the record leads to the production of very high intensity sounds by direct transformation frommechanical variations into acoustical variations of the air immediately surrounding the pickup and the record. Because of the relatively small sizes of the vibrating elements, the major portion of this energy is confined to the high frequency region. 'I'he peculiar conditions under which this sound is generated, in generahleads to considerable distortion in the sound which emanates directly from the pickup and the record. In addition, because of the relatively short wave lengths at the higher frequencieavthe sound due to mechanical vibration of the pickup and the record is not in phase with the sound which emanates from the loudspeaker. For the foregoing reasons, it is highly desirable tosuppress the sound which issues directly from the pickup and record system.

Various attempts have heretofore been made to suppress the sound emanating directly from the pickup and the record. This can be reduced, for example, by enclosing the pickup in a console type phonograph cabinet having 'a lid. However',

due to manufacturing difficulties and the natural4 ytype between the lid and the body of the cabinet has also been suggested, but-this is not practical because a locking system which compresses the seal must be used. Unless this expedient is employed, a slit will be formed between a lesser or greater portion of the cabinet and lid or door system, but the use of a compression loci: has not met with public favor. v

In the aforementioned -copending application of Alexander ,De Burt, there is disclosed and claimed an improved cabinet wherein a series of grooves or channels are formed in the upper edges of the walls constituting the body ci. the' cabinet and upon whiclr the lid or cover of the cabinet rests when in closed position. These channels, in vconjunction with the slit between thebody and the cover of the cabinet, constitute an acoustic iilter which attenuates the higher frequencies. While a system .of this sort provides excellent results, there are certain manufacturingdiilculties involved in forming the nlter in the manner disclosed in the aforementioned copending application, and it is some times diiicult to obtain a filter in this way which provides the desired attenuation.

y The primary object of my present invention is to provide an improved phonograph cabinet 'which will not be subject to the aforementioned limitation.

More particularly, it is an object of my 'present invention to provide, in a cabinet for housing sound-reproducing apparatus such as a phonograph, an improved acoustic filter which can be arrangedicito provide any desired degree of attenuation of the Asounds emanating directly from the record and pickup and normally reaching the ear of the listener'during operation thereof.

Another object of my present invention is to provide an improved cabinet as aforesaid which is simple in construction, is inexpensive to manufacture, which readily lends itself to rapid quantity production, and which is highly eiiicient in use. I

Instead of forming-the grooves or channels in the body of the cabinet itself, as disclosed in the aforementioned Burt application, fI provide, inv

proximity to the body. l' The frame is preferably made of a plurality of interconnected, preformed molding stripsA or sections each of which is shaped to provide one or more channels constituting acoustic c'apacitances of predetermined provide a network which very effectively suppresses the higher frequency sounds radiated directly'from the pickup and the record.

The novel features that I consider characteristic of my invention are set forth with particullarity in the appended claims. The invention, itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, willV best be understood from sired shape, and in the particular form `illustrated in Figs. 1, 2 and 3, each arm 25h has an enlarged upper portion or head 21 which extends the following description of several embodiments the acsponding to the acoustical system of the networkv shown in Figures 1, 2 and 3,

Figure 5 is a sectional view of another formy of my invention,

Figure 6 is a fragmentary section, of still another form of my inventiomeand Figures 7, 8 and 9 are response curves showing the attenuation that may be obtained with my present invention as compared with conventional cabinets.

Referring more particularly to the drawings, wherein similar reference characters designate corresponding parts throughout, I have shown, in Figs. 1, 2 and 3, the cabinet having a body portion A comprised of a plurality of interconnected walls I, 3, 5 land 1, and a cover or lid B hinged to one of the walls, such as the Wall 5,

and adapted to overlie the upper ends of theA walls when the cover B is in closed relation to the body A, as shown in Fig. 1. The body A is of hollow construction and-ds provided with a partition or motor board 9 upon which is mountted a suitable phonograph It lwhich includes a sound-reproducing instrumentality, such as an electrical pickup device I3, and a'turntable I5 .which supports a record I1 in operative relation to the pickup device I3.

Due to manufacturing inaccuracies, warpage in the wood of which the cabinet is made, and other similar causes, there is a small space I9 between the body A and the cover B in practically all cabinets. aggerated in the drawings by having the cover A rest on the hinge 2! and on a pair of rubber or felt bumpers 23. It is through this space that sounds emanating directly from the pickup device I3 andthe record I1 due to the mechanical vibration thereof` pass out to the exterior of the cabinet and cause considerable annoyance, especially at the higher frequencies. f In order to overcome this difficulty, I provide an endless frame member made up of a plurality of interconnected molding strips, one each of which is connected to the upper marginal portions of each of the "walls I, 3, Svand 1. Each of the molding strips of the frame 25 is substantially L-shaped in transverse cross section to provide a horizontal portion or arm 25a (see Figure 3). through which the'strips may be secured in suitable m'anner to ,the respective walls of the cabinet, and a vertical arm 25b which extendsparallel to the associated wall in spaced relation thereto, the upper surface 25e of the forwardly toward its associated wall, this providing, between the arm 25h and the associated wall, a cavity or channel 29 having a relatively wide bottom and which tapers olf to a relatively narrow mouth at the'top. Each of the heads 21 of the arms 25b may also be formed with a channel 30 extending parallel to the'associated channel 291 Referring more especially to Fig. 3, it will be noted that the previously described'construction affords the spaces or space sections I9a and I9b This space has been somewhat exframe 25 of any desired shape, and thus any' frame member 25 being substantially flush with l the upper edges of the walls of the cabinet. The

between the vertical arm 25h of each section of the frame member 25 and the cover B, and also that the overlapping portion of the Acover and any one of the walls of the cabinet have a space I9c therebetween. The spaces I9a, I9b, and I9c are, of course, all in series. The equivalent electrical circuit of the acoustical system of Figs. 1, 2 and 3 is shown in Fig. 4 wherein v v m1 is the inertance of the volume of air immediately inside of the frame 25 and under the cover B, as bounded by the dotted line E in Fig. 3, for example,

r1 is the acoustic resistance of this volume of air,

ma is the inertance of the air .in the space I9a,

112 is fthe acoustic resistance of the air in the space I9a, a

m3 is the inertance of the air iry the space I9b,

-rs is the acoustic resistance of the air in the space I9b, m4 is the inertance of the air inthe space I9c, r4 is the acoustic resistance of the air in the space I9c, m5 is the inertance of the ,volume of air immediately outside of the cabinet in the vicinity bounded by the dotted line F in Fig. 3, rs is the acoustic resistance of this volume of air, mg isA the inertance of the air at the mouth of the channel or cavity 29,

rs is the acoustic resistance offered by the air at the mouth of the cavity 29,

r1 is theq resistance offered by the walls enclosing the volume of air in the lower or larger portion of Ithe cavity 29,

c1 is the acoustic capacitance of the cavity 29,

ca is the acoustic capacitanceof the channel or cavityy 30, and ra is the resistance oii'ered by the walls enclosing the air in the cavity 30.

The values of me, n, r1, ra, ci and c2, as weil asI thevalues of m2, ma, rz, and Ar3 can be easily controlledby making the molding strips of the degree of attenuation may be obtained.

In Fig. 5, I have shown another form of my invention wherein the cabinet A is constituted by a top wall 3l, a back wall 33, a bottom wall 35 an-d end walls y31, the cover B being constituted by a door hinged to one of the end Walls 31 and arranged to swing inwardly between and flush with the ends of the Walls 3|, 35 and 31 when the door B is in closed relation to the body A. The frame 25 is secured to the door B instead of to the walls of the cabinet, and the channel 30 may be formed between the channel 29 and the door B. It will be noted that the molding `members of which the frame 25 is formed are again substantially L-shaped in transverse cross section, the vertical arms being secured to the door B and the horizontal arms vertical arm 25h may be preformed to any de- 75 having the channels 29 and 30 formed therein.

A somewhat simpler, although equally eiective, arrangement is shown in Fig. 6i VIn this modification, which employs a cabinet and door similar to that shown in Fig. 5, thev frame 29 is secured to the top and bottom walls 3|. and 35 and to the end walls 31, with one arm of each molding member spacedfrom the associated wall to provide only the cavity 29. The cavities or channels 30 may be formed either in the door B or in the walls of the cabinet, and, in the particular form illustrated '1n Fig. 6, I have shown one such channel formed in the lower'- edge of the door B and another formed in the overlap, ping portion of the top wall 3|. i

A comparison of the curves in Figs. 7, 8 and 9 will show the advantages of my present invention. In Fig. '7,l the curve I shows the response frequency characteristic of a conventional door.

and cabinet arrangement, the response being arbitrarily chosen as unity. The curve II in this figure shows the response frequency characteristic of a cabinet having my improved acoustic network incorporated therein as compared with the response of the conventional door and cabinetshown by curve L l f In Fig. 8, the curve III shows the response frequency characteristic of a sound source within a cabinet of conventional design, and curve IV shows the response frequency characteristic of v the same cabinet and sound source where a perlfect seal is provided between the door and the cabinet.

Figure 9 shows a set of experimental curves, the curve V, like the curve III of Figure 8, showing the response frequency characteristic of. a sound source within a cabinet of conventional design, and the curve VI showing the response frequency characteristic of the same cabinet and sound source after being equipped with an acoustic network in accordance with my present invention. It will be noted that the attenuation shown by curve VI is considerable, particularly at the higher frequencies, and that it compares most favorably with the curve IV of Fig. 8.

From the foregoing description, it will be apparent to those skilled in the art that I have provided a novel cabinet and acoustic filter arrangement which will effectively' suppress the annoying higher frequency sounds normally associated with phonographs. Although Iv have tion, it will be apparent to those skilled in the art that many other variations thereof are pos'- sible and I therefore desire it to be understood vthat my invention is Inot to be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

shown and described several forms of my invenl respect to said body, the'space between said body and cover permitting the passage of sound.

one cavity constituting an acoustic capacitance v for sound waves emanating from said apparatus.

2. A cabinet'for housing sound-reproducing apparatus comprising a body part, a cover part movably associated therewith,A said parts having portions thereof in overlapping and slightly spaced relation when said cover is closed: with respect to said body, the space between said body and cover permitting 'the passage of sound waves emanating from said apparatus out to the exterior of thecabinet, and means connected to one of said parts in slightlyfspaced relation to the other of said parts to provide a second space therebetween in series with said first space, said means being constructed and arranged to also provide at least one acoustic capacitance for the sound waves` passing through said spaces, and said capacitance cooperating with the acoustic resistances and vinertances offered yto said sound waves by said spaces to constitute an acoustic filter for attenuating' at least certain o'f said waves. l

3. The invention set forth in claim 2 characterized in that said capacitance is in shunt relation to said'spaces. v

4. The invention set forth in claim 2 characterized in that said means is constituted by a substantially L-shaped member one arm of which is secured to the body of the cabinet with the other arm thereof in parallel relation to and spaced from said body, the space between said member and said body providing a cavity constituting said capacitance.

5. A cabinet for housing sound-reproducing apparatus comprising a body part, a cover part movably associated therewith, saidparts having 1 portions thereofiny overlappin Vand slightly spaced` relation when said cover is closed with respect to said body, the space .between said bodyL and said cover permitting the passage of sound waves emanating from said apparatus out to the exterior of said cabinet, and an 'endless frame member secured to one of said parts in slightly spacedl relation to` the otherof said parts to provide asecond space through which's'aid waves will pass, said spaces being .in series with each f other, and said frame having a portion in spaced 4relation to the part to which it is secured to Y with respect to said body, the space between saidbody and said cover permitting the passage of sound waves emanatingy from said. apparatus out to the exterior of said cabinet, and

an endless frame secured to one/Lof said -parts,.

said frame being substantially iiush with those ends oi said last-named part with which the ends of the other of said parts cooperates to provide a second space which is between said frame and said other part, and certain portions -of said frame being spaced from said first-named part to provide at least one cavity .therebetween in shunt relation to said first and second-named spaces, said cavity and said spaces cooperating to provide an acoustic filter for attenuating at leastcertain of said waves. n

7. A cabinet for housing sound-reproducing apparatus comprising a body part constituted by a plurality `of interconnected walls, a cover part movably associated therewith, said parts having portions thereof in overlappin! and slightly spaced relation when said cover is closed Iwith respect tosaid body, the space between said body and said .cover permitting the passage of sound waves emanating from said apparatus out to the exterior of said cabinet, and an endless frame secured to said walls interiorly of the cabinet, said frame being substantially iiush withthose ends of said walls with which said cover cooperates whereby to provide a second space which is between said cover and said frame, and certain portions of said frame being spaced from said walls to provide a cavity therebetween in shunt relation to said firstI and second-named spaces, said cavity and said spaces cooperating to provide an acoustic filter for attenuating at least certain of said waves.

8. The invention set forth in claimf7 characterized in that said frame is constituted by a. plurality of interconnected members each of substantially L-shaped cross section and each having one of its arms connected to one` wall of said body part, the other arm thereof being spaced from the cooperating wall to provide said cavity.

- 9. The invention set forth in claim 7 characterized in that said frame is constituted by a plurality of interconnected members each of substantially L-shaped cross section and each having one of its arms connected to one wall of said body part, the other arm thereof being spaced from the cooperating wall to provide said cavity and being so shaped that said cavity 'is narrower at one end than at the opposite end.

l0. Illhe invention set forth in claimy 7 characterized in that said frame is constituted by a plurality of interconnected members each'of A substantially L-shaped cross section and each having one of its arms connected to one wall of said 4body part, the other arm thereof being spaced from the cooperating wall to provide said cavity and being so shaped that said cavity is narrower adjacent said cover than at its opposite end.

11. 'I'he invention set form in claim 7 char` acterized in that said frame is constituted by a plurality of interconnected members each of substantially L-shaped cross section and each having one of its arms connected to one wall of said body part, the other arm thereof being spaced from the cooperating wall to provide said cavity, and characterized further in that saidK other arm of each of said members i`s provided with a channel in parallel relation to said cavity. 12. 'I'he invention set forth in claim'5 characterized in that an additional cavity is provided in said frame member in shunt relation to said first-named cavity.

13. 'I'he invention set forth in claim 5 characterized in that an additional cavity is provided Iin at least one of said parts in shunt relation to said first-named cavity.

14. 'Ihe invention set forth in claim 5 char- I acterized in that .at least one additional cavity is provided in said body in proximity to said cover and at least one othercavity is provided in said cover in proximity to said body, said additional cavities being in shunt with said first-named cavity.

' HARRY F. OLSON. 

